CLAYTON -- Burning for more than a day, a wildfire outside Mt. Diablo State Park has grown to nearly 4,000 acres, but by Monday evening officials were more optimistic about the possibility of an earlier-than-expected containment.

The fire has been burning near Morgan Territory Road since about 2 p.m. Sunday, and rose dramatically in acreage early Monday afternoon when it reached the peak of the mountain.

The fire grew to 3,718 acres Monday, and was 20 percent contained as of 3 p.m. Fire officials said as of 8 p.m. that the blaze had just "stopped," that the total number of acres consumed had not grown since the afternoon, and that containment remained at about 20 percent.

Cal Fire officials called in additional resources to battle the growing blaze, known as the Morgan Fire, which is threatening structures and has already damaged a remote outbuilding.

Though the sharp rise in acreage gave fire crews a scare early in the afternoon, by 8 p.m. Monday, the spread had waned, and the outlook improved considerably.

"It's looking much better tonight than it was this afternoon," said Julie Hutchinson, battalion chief for Cal Fire. "It was spreading very quickly, and by mid-afternoon, it got to a point where it just stopped."

Three firefighters had suffered minor injuries, the most recent on Monday afternoon, Hutchinson said. There was no information available on the specific nature of their injuries.

Hutchinson said crews have their eye on some "weird weather" coming in from the north, and said that the combination of high heat and low humidity could potentially raise a red-flag warning.

The National Weather Service forecast highs of 90 to 95 degrees Tuesday with winds between 10 and 20 mph expected in the afternoon.

The Bay Area Air Quality Management District issued a smoke advisory for Contra Costa, Alameda and Santa Clara counties, and reminded residents to limit their exposure to smoky air and advised those with asthma or lung and heart conditions to talk to their doctor about possibly avoiding the areas affected by smoke.

A team of firefighters from across the state came in at 6 p.m. to take over all operations, said Steve Kaufmann, spokesman for the Incident Management Team, whose strategy for the overnight hours is to draw a box around the fire and attempt containment from within those parameters.

"The winds picked up, so we've gotta keep a watch on that," Kaufmann said. "There are some sensitive areas up there."

Kaufmann, a 17-year firefighter from the Ventura County area, notes that this is the sixth major fire the Incident Management Team has been on this year, and that it has been a particularly busy season because of the abundance of dry fuels like wood and brush. In that way, the Morgan fire is directly tied into what they are experiencing statewide, and Kaufmann said the busy season has dealt the crew a great deal of experience working in dramatic fire conditions.

"It definitely makes us more proficient at what we do," Kaufmann said.

Rein said about 100 homes had been evacuated as of Monday morning. Those homes were in danger as the fire shifted south Sunday, away from Clayton and toward the summit of Mount Diablo, Hutchinson said.

"It's kind of burning up and around" Mount Diablo, she said.

Officials used two air tankers to drop fire retardant on the growing fire starting about 8 a.m. Monday, Rein said. Three helicopters were also making water drops.

Dennis Rein, an information officer for the Moraga-Orinda Fire District, said 250 firefighters had been on the line overnight and were being replaced Monday morning with 700 new firefighters. Crews are gathering at Camp Parks in Dublin and are arriving from all over the region and California, he said.

East Bay Regional Park District fire Lt. Mark Tait, 42, of Danville was among the replacements. The 15-year veteran said that in July, he was on the line fighting the Aspen Fire in the Sierra National Forest-High Sierra Ranger District for 11 days. He was home for eight hours before he was then dispatched to the Rim Fire in Yosemite for 12 days.

After a week at home, he's now being dispatched to the Morgan Fire.

"This is pretty standard stuff" this time of year, he said, noting that "usually it starts down south" in Southern California, where warm winds fuels summer fires.

Describing the challenges of fighting back-to-back fires, he said, "You rely on your training and a lot of coffee. A lot of coffee.

"Also you have to have a lot of support at home," he said before rushing off to gear up.

"Our firefighters are away for their families more, so that's probably the biggest toll," adds Kaufmann. "You miss birthdays, anniversaries. You miss Christmases. These are important days for the family unit."

And while the blazes weigh heavily on firefighters and their own families, Kaufmann says the hardest part is often watching other families return to the damage and devastation surrounding their homes for the first time — seeing what's left, and trying to make sense of it.

"It drives it home as a human being," Kaufmann said. "All of our firefighters have empathy for that."

Trucks pulling horse trailers snaked up the mountain and back down on Sunday night, carrying animals to safety out of the fire zone.

Homeowners in the Diablo Downs neighborhood of Clayton, off Mitchell Canyon Road, have taken in seven horses. Larry and Valerie Sterling, who are members of the Concord Mt. Diablo Trail Ride Association, took in four horses and Pam Hall took in two horses and a mini owned by Mike and Paulette Probst, who also evacuated four dogs and a cat.

"The horse community is really pretty tight," said Larry Sterling, as he fed hay and carrots to his new charges. "All over Clayton, you've got horse trailers hooked up and ready to go, ready to help people."

The Probsts and some other families stayed in sleeping areas of their trailers overnight, but may go stay with friends and leave their horses if they are not allowed to return to their homes tonight, they said.

"We had a neighborhood sleepover," Valerie Sterling said with a smile.

At the American Red Cross evacuation center at the Clayton library, spokesman Jim Mallory said three families were put up in hotels overnight and Salvation Army volunteers served lunch. Mallory urged anyone who wants to make a donation to visit www.redcross.org.

Larry and Caryn LeGate said they left their home on Trail Ride Sunday afternoon just after the fire started to go out of town. When they returned at night, firefighters wouldn't let them go back, so they stayed in a hotel. Monday morning, firefighters allowed them to drive back up to their home, where they retrieved their toothbrushes and some clothes, they said.

The couple said they wouldn't feel safe staying in their home right now because smoke could been seen coming over a nearby ridge.

Laura Hoffmeister, assistant to the City Manager in Clayton, said about 20 people came to the evacuation center Sunday, including many who needed to recharge their cell phones as they tried to make arrangements for places to stay.

She said horses had also been evacuated to Heather Farm Park in Walnut Creek and to the Antioch fairgrounds. One family, she said, had to evacuate several sheep and goats before they returned to get their horses.

Renae Parker, who owns Buena Amor Stables in unincorporated Pleasanton, said she took in seven horses last night and has room for 20 more. She urged anyone who is interested to call her at 925-248-1990.

"If I can help anybody out," she said, "it's awesome."

At the Equestrian Center of Walnut Creek, smoke could be seen in the distance, but the air was clear overhead. Mary Stewart, who is on the organization's board of directors, said someone will be at the center around the clock and there is plenty of room for more horses who may need to be evacuated.

Four horses arrived Sunday night and two more, plus eight mini horses, arrived Monday. The group also received donations from Concord Feed, El Sobrante Feed and Home Depot, she said.

"From this angle, this is pretty ominous," Stewart said, as she watched plumes of black and white smoke over hills in the distance. "We're open and we're available and we have lots of room."

Sharon Giampapa evacuated her two horses to the center Sunday, along with two others that were boarding at a facility on Morgan Territory Road.

"We saw the flames and ash was coming down," she said. "We don't want to take the horses back until I know they've got it under control because evacuation is very stressful for the horses and the people."

She said the horses' eyes were wide and they were racing up and down in the pens because the helicopters were flying overhead.

"They were snorting and bucking and racing around in the paddocks," she said of the horses. "They were whinnying and rocking in the trailer. But they calmed down last night and this is far enough away from the fire that we don't have to worry about evacuating again."

Becky Walker said she decided to evacuate her horses after seeing the fire directly across the street from their barn near Morgan Territory and Marsh Creek roads. Bob Beck, co-founder of Angels for Minis mini horse rescue in Walnut Creek, also brought seven minis from Blue Oak Ranch in that same area to the center on Monday afternoon after the fire started getting too close for comfort.

"It was just across the road and it just seemed like it was time," he said. "We're not taking them back until it's safe. So, we're camped out in our RV."

The Contra Costa County Fairgrounds in Antioch is also set up to receive evacuated livestock and pets from the fire. Some horses are expected to arrive later, said fairgrounds manager Robert Williamson.

As of early Monday afternoon, the only animals at the 80-acre facility were five chickens, two ducks and four cats. One of the chickens had already laid an egg, a sign of adjustment to new surroundings, said maintenance supervisor Mack Reninger.

"She didn't bring it with her," he said.

The fairgrounds housed evacuated animals during the last big Mount Diablo fire that occurred in 1977, said Williamson.

"We were ready to (receive animals) last night in case in the middle of the night they needed some place to go," he said.

The fairgrounds has also received calls from people who want to volunteer their services to help care for evacuated animals once they arrive and from feed stores that want to help out, Williamson said.

Alameda County Fire spokeswoman Aisha Knowles, who was stationed at Camp Parks, said there were no immediate plans for more evacuations.

She said firefighters would be working Monday to create an eight-mile containment zone by hand and using bulldozers.

"The biggest challenges are access, the combination of very dry fuels, steep and rocky terrain, and having been through a drought," she said.

She said the magnitude of the fire should be a reminder to residents to make sure they maintain a defensible space around structures. In areas where homes lie close to wildland, this means vegetation and dry brush should be cleared in a 100-foot area around homes and other buildings.

"A large fire like this emphasizes that fire safety is everyone's business," Knowles said.

The San Ramon Valley and Dublin school districts told students to stay indoors for after-school sports practices and instructed students to stay indoors during recess and physical education classes.

Terry Koehne, a spokesman for the San Ramon Valley district, said sports teams could cancel practices if they wanted to and he anticipated the district would cancel swim practices before school Tuesday.

"It looks like the air quality is probably going to get worse," he said, "and the fire probably isn't going to be controlled by then."

Dublin school Superintendent Stephen Hanke said the district had instituted its rainy day procedures because of the smoky air.

"At the time we checked it out, the level of pollution in the air was moderate," he said. "But, we're getting some reports of skies that don't appear to be clear. We're going to watch this to see if conditions change."

Camp Parks spokesman Dan Gannad said the U.S. Army mobilization and training center for reserve forces was set up Monday morning as the base camp where firefighters will be able to check in, sleep, eat, pick up supplies and more.

"We have the facilities and the support structure," he said. "In the middle of all this civilization we have all this open land and we're happy to provide it."

Knowles said support and personnel for the camp is being provided by local and state fire agencies, with a Cal Fire specialized team expected to take command Monday evening.

The fire is the largest near Mount Diablo in recent memory. Many longtime locals remember the 6,000-acre fire that started on the mountain on Aug. 2, 1977. Former Mayor Pete Laurence said he was driving on Kirker Pass Road when he saw a lightning bolt strike the mountain and spark the fire. It burned for more than 82 hours, leaving the mountain a "a battlefield with charred skeletons of trees," according to a report in the Oakland Tribune at the time.

"It was worrisome because Mother Nature was having her way with the mountain," Laurence said.